Cataract

A cataract is an opacity in the crystalline lens of the eye that scatters or blocks light entering the retina, producing blurred, dim, or colour-faded vision. It is the most common cause of blindness worldwide, and it is among the most frequently performed surgeries in medicine. The lens is a transparent structure made largely of proteins that focus light. Because the lens has no blood supply and its proteins are long-lived, damage accumulates over decades. Aging, diabetes, ultraviolet exposure, and other factors can cause proteins to clump or chemically change until the lens becomes cloudy. The condition is studied through optics, biochemistry, epidemiology, and surgery.

This entry covers the anatomy and biology of lens opacity, the main types and causes, and the risk factors and epidemiology reported in global studies. It then describes symptoms, diagnosis, and the limits of nonsurgical management. Surgical removal of the cloudy lens with implantation of an artificial lens is the only widely accepted treatment, so the entry examines surgical techniques, lens implants, complications, and outcomes in detail. It also addresses cataract in children, the global access gap that leaves most avoidable cases untreated in low- and middle-income countries as reported by the World Health Organization, and the economic and social consequences for patients and families.

The final sections trace the history of cataract treatment and its terminology, then turn to emerging research on drugs, drug delivery, regenerative therapy, and digital tools, and close with unresolved questions and debates about causes, prevention, and the allocation of surgical resources.

Lens Anatomy and the Nature of Opacity

The crystalline lens is a biconvex, transparent body suspended behind the iris, and its main job is to focus light onto the retina. It is also avascular. Unlike the majority of tissues, the post-natal lens has no direct blood supply. Instead, it obtains its nutrients mainly from the aqueous humour, which bathes the anterior face of the lens. The aqueous humour is secreted by the ciliary body and contains all the ingredients needed to sustain the lens. Oxygen reaches the lens by diffusion from the iris and retinal vasculature through the aqueous and vitreous humours, and the lens sits in one of the most oxygen-poor environments in the body, with a pO2 of 11 mm Hg. Its energy supply is largely glycolytic: most of the glucose metabolized in the lens is handled by anaerobic glycolysis. Metabolic activity is concentrated in the outer tissue, since this metabolic activity is primarily limited to the epithelium and superficial fibers of the lens, while the lens nucleus lacks such metabolic activity. Because no blood-borne cells or replacement materials arrive, damaged proteins cannot be cleared or replaced from outside the tissue, which is a central reason repair is limited.

Transparency depends on the internal organisation of the fibre cells. Lens fibres are tightly packed with little intercellular space, and their cytoplasm is dominated by proteins called crystallins, which account for approximately 40% of the net weight of the fiber. The α-, β- and γ-crystallin families make up 90% of water-soluble proteins of the mammalian lens. During fibre differentiation, synthesis and short-range ordered packing of crystallin proteins give the tissue its transparent and refractive character. Organelles are also removed from maturing fibres, and this contributes toward lens transparency through formation of an organelle-free zone. The crystallins are unusually resistant to clumping: these proteins are extremely soluble and resist aggregation for decades, even under crowded conditions. Alpha-crystallin also acts as a molecular chaperone that helps prevent other proteins from precipitating.

The physical basis of opacity lies in how light interacts with the lens's internal structure. The lens focuses light because its proteins are arranged to produce a smooth refractive index gradient. When that order breaks down, light is no longer directed cleanly to the retina. With time, the modified crystallins aggregate, causing the lens to increasingly scatter light on the retina instead of focusing light on it. Scattering becomes significant once the particles are large relative to the wavelength of light: light scattering and opacity also can occur if there are significant high molecular weight protein aggregates roughly 1000 Å or more in size. The insoluble fraction of lens protein also rises with age and cataract formation: the percentage of insoluble protein increases as the lens ages and as a cataract develops. Changes in the fibre membranes contribute as well, since with age and cataract formation, the concentration of α-crystallin in the eye lens cytoplasm decreases with a corresponding increase in the membrane-bound α-crystallin, accompanied by increased light scattering.

Because the lens keeps growing, its oldest material is retained at the centre. The epithelial cells continue to produce new cortical lens fibers, yielding a slow increase in size, weight, and density over the years. Growth follows a distinctive pattern in humans. In most species, this takes place through a single self‐limiting (asymptotic) process, whereas human lens growth takes place through a unique biphasic process, not observed in any other species. The result is two distinct tissue compartments in the adult human lens, the fixed‐size nucleus and the continuously growing cortex. Newer fibres are laid over older ones, so lens fibers are successively younger as they are situated away from the central lens nucleus. The central nucleus therefore holds material that has been in place since before birth, and unlike other proteins in the cell, crystallins, once synthesized, remain in the lens for the individual's lifetime. This means that the molecular changes the lens accumulates are not diluted by turnover. Age-related modifications such as oxidation, deamidation, truncation, glycation, and methylation are cumulative and affect crystallin structure and function. Over decades, the nucleus also becomes denser: as the older cells become more tightly packed, the nucleus becomes denser and harder.

Types and Locations of Lens Opacity

Age-related cataracts are commonly sorted by where in the lens the clouding begins. The three main categories are nuclear, cortical and posterior subcapsular. Each affects a different layer or region of the lens, and each produces a different pattern of visual symptoms and progresses at a different pace. Mixed forms, in which several regions are affected at once, are common in practice.

Nuclear sclerosis and nuclear cataract

Nuclear cataract is the most frequent form. It begins in the central nucleus, the oldest part of the lens, where the tissue gradually hardens and takes on a yellow tint. This change is a normal feature of ageing, known as nuclear sclerosis, and it becomes a clinically significant cataract only when it is severe enough to impair vision. Progression is usually slow and can take years. Changes in the lens proteins of the nucleus raise its density and refractive index, which shifts the eye toward myopia. This myopic shift often produces a paradoxical, temporary improvement in near vision: people who had needed reading glasses may find they can read without them for a period. As the nucleus continues to change, distance vision blurs and colours appear faded or duller, and the cataract can extend into other regions of the lens. Because the refractive change can alter the prescription repeatedly, nuclear cataract is often the form that prompts frequent changes in glasses before surgery is considered.

Cortical cataract

Cortical cataract develops in the cortex, the outer zone of the lens. It typically starts at the periphery as wedge-shaped opacities, which then extend inward like spokes toward the centre. These spokes scatter light unpredictably, so patients commonly report glare from headlights and bright lamps, halos around light sources, and problems with depth perception. Because the periphery of the lens is affected first, central vision can remain fairly clear for a long time, and patients may not notice the change until the spokes reach the visual axis. The speed of progression varies considerably: some cortical opacities advance over months, while others take years. Diabetes is more often associated with this type than with the others.

Posterior subcapsular cataract

Posterior subcapsular cataract forms in the back layer of the lens, just beneath the capsule, and lies close to the point where light converges. It is less common than the nuclear and cortical types overall, but it appears more often in younger people. It tends to develop over months rather than years. Its main risk factors include diabetes, corticosteroid use, ocular trauma, previous eye surgery and radiation or chemotherapy. Because the opacity sits near the focal point of the eye, it disproportionately affects near vision and reading, and it commonly causes glare and halos, particularly in bright light. Sources differ on whether its onset is best described as sudden or as rapid but gradual, a discrepancy that likely reflects variation in individual cases.

Cataract in dogs and other animals

Cataract is also one of the most common causes of vision loss in dogs. In purebred dogs, the leading cause is inherited disease, and over 150 breeds are shown or suspected to be affected. Some inherited forms follow an autosomal recessive pattern, in which an affected dog carries two copies of a mutation, while carriers are clinically unaffected but can pass the mutation to their offspring. Breeds such as the Labrador retriever, American cocker spaniel and poodle are among those considered more susceptible. Inherited cataracts usually appear when dogs are young to middle-aged. Diabetes mellitus is the second leading cause in dogs. In the diabetic lens, the enzyme aldose reductase converts excess glucose into sorbitol, which draws water into the lens. The resulting swelling disrupts lens fibres, and oxidative stress contributes to the damage. Diabetic cataracts in dogs form rapidly: one retrospective study found that half of affected dogs had developed cataracts by about 170 days after diagnosis, and roughly 80 percent by 16 months. Lens-induced uveitis and secondary glaucoma are frequent complications, and glaucoma is difficult to control in these animals. Cats with diabetes rarely develop cataract, because their lenses contain relatively little aldose reductase. Other canine causes include trauma, nutritional imbalance, chronic intraocular inflammation and progressive retinal atrophy. Surgical candidacy in dogs depends on the health of the cornea and retina, since a healthy retina is needed for the dog to regain useful sight.

Causes and Biological Mechanisms

Age-related lens opacity is not traced to one lesion. Several chemical processes act on the same long-lived proteins of the lens, and they probably reinforce one another. Oxidation, sugar-driven modification, aggregation and disturbed ion handling each contribute to the loss of the lens's transparency.

Oxidative damage is widely regarded as a major contributor. The lens interior has low oxygen tension, so the physiological source of the reactive oxygen species is not fully clear. Even so, low-level oxidants combined with photo-oxidation of ultraviolet filters may be enough to injure proteins. The lens normally relies on reduced glutathione and ascorbate (vitamin C), together with enzymes that regenerate them, to keep redox balance. With age, these defences weaken while markers of lipid peroxidation rise. Oxidation of methionine and cysteine residues in γ-crystallins destabilises their folding and alters their solubility.

Ultraviolet radiation adds a second, more direct source of damage. Ultraviolet-B is largely absorbed by ozone, the eyelids and the aqueous humour before it reaches the lens, whereas ultraviolet-A penetrates further into the lens tissue (ultraviolet light). Aromatic amino acids in crystallins absorb in the ultraviolet-B range, and the lens contains endogenous filters such as 3-hydroxykynurenine derivatives that absorb energy and protect proteins. Over time these filters become bound to proteins, which reduces their protective supply. Some of them can also act as sensitisers that increase protein damage under light exposure. UV-induced cross-linking of α-, β- and γ-crystallins changes their solubility and promotes light-scattering aggregates.

Chemical modification of proteins accumulates because lens fibre cells cannot replace their proteins. Glucose and other reducing sugars, as well as reactive dicarbonyls such as methylglyoxal, react without enzymes with lysine and arginine side chains. This forms early adducts and then advanced glycation end-products. Hyperglycaemia, as in diabetes, accelerates this process. In the lens, high glucose also activates the polyol pathway, in which aldose reductase converts glucose to sorbitol, creating osmotic stress. Glycation of α-crystallin weakens its chaperone activity, so partly unfolded proteins are less likely to be protected. Deamidation is a slower, age-related change in which asparagine and glutamine residues convert to aspartate or isoaspartate. This adds a negative charge and can disturb the local packing of the protein.

These modifications matter because of the physical consequences of protein disorder. Crystallins are present at very high concentrations, reported as 250–400 mg/ml and about 90 percent of the total protein content of fibre cells, and they must remain soluble for the lifetime of the lens. Transparency depends on short-range order among these densely packed proteins. When proteins unfold, cross-link through disulfide bonds, or form amorphous aggregates, the resulting fluctuations in density and refractive index scatter light. Insoluble, high-molecular-weight protein fractions increase with age and are especially prominent in the nucleus. Some genetic mutations act through the same route. For example, an internal disulfide in a mutant γD-crystallin is sufficient to drive aggregation under physiological conditions.

Disturbed ion balance affects the cells that maintain the lens. Calcium accumulates in the lens with age, and calcium-activated calpain proteases can cleave crystallins and damage cell membranes. Experimental selenite cataract, widely used as a model, shows that oxidative insults disrupt calcium regulation in lens epithelial cells and activate calpains. Membrane transport systems that move ions across cell membranes also depend on enzyme activity, which declines when oxidation and modification accumulate. Ultraviolet light and oxidants therefore act not only on proteins but also on the ionic environment that keeps those proteins soluble.

Risk Factors and Global Epidemiology

Age is the dominant risk factor. Cataract is characterized by the progressive opacification of the eye's crystalline lens and disproportionately affects older adults, with both incidence and severity increasing significantly after the age of 60. In GBD 2021 data, prevalence also rises with age and peaks in people aged 95 and over (Prevalence increased with age, peaking in those aged ≥95 years.). Because populations are ageing, the number of affected people has grown even where rates have fallen. The GBD 2021 analysis reports that prevalent cases rose from 32.8 million (95% UI: 26.9–45.4 m) in 1990 to 82.2 million (95% UI: 66.6–101.7 m) in 2021, while the Age-Standardized Rate (ASR) of DALYs decreased, the overall cataract Number still showed an increasing trend. Projections in the same dataset extend this rise to 2050 (a continued rise in global cataract cases and DALYs by 2050 under current demographic and epidemiological trends). One separate GBD-based forecast, using a shorter horizon, instead anticipated a gradual decline in the global burden of cataract over the next nine years, so the direction of near-term change is not uniform across analyses.

The established modifiable associations are diverse. Diabetes increases the risk for all types of cataracts. Systemic and inhaled steroids increase the risk of posterior subcapsular cataracts. Tobacco is dose-related: cigarettes and smokeless tobacco are both dose-related risk factors for cataract development. Alcohol has been reported as a risk factor particularly in women, and extensive sunlight exposure, i.e., photo-oxidation secondary to UV-B. Risk is dose-related. Air pollution is also prominent: in GBD-based work, PM_2.5 and UVR were positively associated with age-standardised burden, and key contributors included air pollution and metabolic disorders, particularly in low-SDI regions. Individual-level estimates of these associations vary between studies and populations, and several of them are better supported for some subtypes (such as posterior subcapsular cataract with steroids) than for others.

Burden is unevenly distributed by sex and region. Females had consistently higher ASPRs than males across all age groups and regions. A 2010 analysis found that cataract caused 35.5% (95% UI: 31.0–39.1) of blindness in women, compared with 30.1% (95% UI: 25.2–33.7) in men. Regionally, South Asia and sub-Saharan Africa bearing the highest burden due to limited surgical access. In 2020, the age-standardised prevalence of cataract-related blindness among adults aged 50 and over was South Asia (2.23% [95% UI: 1.89, 2.61]) and Sub-Saharan Africa (1.49% [95% UI: 1.24, 1.78]), the two highest regional values.

The share of blindness attributed to cataract differs considerably among sources. A 2020 meta-analysis estimated that cataract caused 39.55% (95% UI: 33.48, 46.34%) of all blindness in 2020 worldwide. The GBD estimate for the same year, cited in that paper, was approximately 15.2 million cases [95% Uncertainty Interval (UI): 12.7–18.0) that comprised 45% of global blindness, and the WHO figure most often quoted is 51 percent of world blindness. Several factors account for the spread. Estimates differ in whether they count blindness alone or moderate and severe visual impairment (MSVI): the same meta-analysis found that cataract caused 28.30% (95% UI: 24.32, 32.54) of all cases with MSVI in 2020 worldwide. The share also moves over time as other causes change; between 1990 and 2010, for example, the percentage of global blindness caused by cataract decreased from 38.6% (35.2–42.0) to 33.4% (29.6–36.4), partly because the numbers of people blinded by trachoma, onchocerciasis, and vitamin A deficiency have tended to decrease. Regional and national shares also vary widely, with one summary noting that the proportions of cataract blindness in Paraguay and Panama are 44% and 66%, respectively. Differences in modelling methods, reference years, and the use of age-standardised or crude rates contribute further to the range.

Symptoms and Natural Course

Cataract usually causes a painless, gradual loss of clarity rather than a sudden change. The most common complaints are blurred vision, colours that look duller or yellowed, and increased glare and halos around lights. The optical reason is that a cloudy lens scatters incoming light instead of focusing it cleanly on the retina, so a headlight or streetlight may appear to be surrounded by rings or starbursts. Night vision is usually the most affected, because the pupil is wider in dim light and more light passes through the opaque regions of the lens, which lowers contrast. Reading in bright light can also become harder, and many people need stronger lighting or larger print.

Changes in refraction are often among the first signs. In nuclear sclerosis, the hardening centre of the lens increases its refractive index, which shifts the eye toward nearsightedness, a process called myopic shift. A person who had been hyperopic or presbyopic may therefore read without glasses for a period, a phenomenon known as "second sight". In a Wisconsin-based analysis, people without nuclear cataract showed a small average hyperopic drift each year, whereas a myopic shift appeared only in those whose nuclear opacity was at grade 4 or higher. Second sight is temporary: it does not restore the accommodation lost to presbyopia, and distance vision tends to deteriorate as the opacity advances. Because the prescription keeps changing, patients often notice that they reach for different pairs of glasses, and a clinical study of people seeking cataract surgery found that a substantial share had a measurable myopic shift at the time of evaluation.

Monocular diplopia, the perception of a doubled image in one eye alone, is a recognised though less typical symptom. Monocular double vision is usually caused by refractive or optical problems in the front of the eye, and cataract is among the common causes alongside uncorrected astigmatism and tear-film abnormalities. A simple pinhole test often improves the symptom, which helps distinguish it from other causes. By contrast, double vision that disappears when either eye is covered is binocular and points to misalignment of the eyes, which is a different problem. Sudden onset of double vision, or double vision accompanied by flashes, a curtain-like shadow or pain, calls for urgent examination because it may signal a retinal or neurological problem rather than a lens change.

Cataracts are often asymmetric, so the two eyes can be affected to very different degrees. The more opaque eye may produce a blurrier, dimmer or differently coloured image than its partner, and the patient may rely on the better eye for most tasks without noticing the imbalance. Lenses prescribed to correct each eye separately can therefore differ, and the mismatch can make glasses feel uncomfortable. In many people the cataract progresses in one eye before the other, and the eyes are not always assessed at the same stage.

Progression is gradual and uneven. Symptoms generally worsen over months to years, and people often adapt to the decline before recognising how much their vision has changed. The speed depends largely on the type and density of the opacity: nuclear changes tend to advance slowly over many years, while mixed patterns that combine nuclear, cortical and posterior subcapsular changes can cause glare and near-vision problems earlier than the overall stage would predict. Other factors, including age, diabetes and the presence of other eye disease, also influence how quickly function declines, but there is no fixed timetable that applies to all patients. Because of this variability, the decision to operate is based mainly on functional difficulty in daily life rather than on the stage of the opacity alone.

Diagnosis and Clinical Grading

Separating lens opacity from other causes of blur

Diagnosis is by examination with the eye dilated. Visual acuity is measured first, but a low reading does not show where the problem lies. Refraction is therefore central. An uncorrected or changing refractive error, corneal disease, or retinal disease can all produce blur that resembles a lens opacity. If vision improves with a pinhole or a new lens prescription, the cause is probably not the lens. A lens opacity usually keeps acuity reduced even after the best refractive correction is found. Where no slit lamp is available, examination of the red reflex through the dilated pupil, with the ophthalmoscope held about 30 cm away, can help identify early cataracts.

Slit-lamp and fundus examination

The slit-lamp microscope gives a magnified view of the cornea and lens. Slit-lamp examination provides more details about the character, location, and extent of the opacity. Examiners record whether the haze is nuclear, cortical, or posterior subcapsular, and how dense it is, using a standard grading chart. The two main groups are scored differently. Nuclear cataracts are graded according to their color and opacification using slit lamp examination. Cortical and posterior subcapsular cataracts are graded instead using retroillumination to evaluate the degree to which the intrapupillary space or posterior capsule are obscured.

Dilation also permits inspection of the retina and optic nerve. This step matters because retinal evaluation checks for other causes of vision loss, such as macular degeneration. Dilated fundus examination is also used to rule out glaucomatous and other optic nerve changes, which can coexist with a cataract and affect surgical planning.

Standardised grading systems

The Lens Opacities Classification System III (LOCS III), introduced in 1993 as a subjective grading system for cataract using slit lamp, replaced LOCS II. Its developers aimed to correct unequal intervals between standards, only one standard for color grading, use of integer grading, and wide 95% tolerance limits. The system uses reference photographs: six slitlamp images for grading nuclear color (NC) and nuclear opalescence (NO), five retroillumination images for grading cortical cataract (C), and five retroillumination images for grading posterior subcapsular (P) cataract. Grades are placed on a decimal scale, and the standards have regularly spaced intervals on a decimal scale. Reproducibility was tightened as a result; for example, the tolerance limit for nuclear opalescence was reduced to 0.7. Slit-lamp grading is not perfect, however. One validation study found 95% tolerance limits between 0.9 to 1.8 in one patient set.

Nuclear grades also track physical size. In a direct-measurement study, nuclear thickness, nuclear diameter, and age all increased significantly with increasing LOCS III grade of the nucleus. The authors concluded that these data can be helpful in adjusting machine parameters during phacoemulsification. In research, grading thresholds are set for specific purposes. One cohort used NO3 designated as the threshold for a mature cataract. LOCS III has also been applied to characterise radiation-induced cataract after proton therapy for uveal melanoma. Grading has begun to be automated: one deep-learning project used 206,574 cataract frames from 1812 cataract eye videos, with ophthalmologists grading the nuclear cataracts using the cataract grading scale of the World Health Organization.

Preoperative biometry

Biometry measures the eye's dimensions so that the lens power can be chosen. The main inputs are axial length, corneal curvature, and anterior chamber depth. Axial length (AL), which refers to the length of the eye from the anterior surface of the cornea to the internal limiting membrane (ILM) of the retina or retinal pigment epithelium (RPE), is a reading required in all power calculation formulas and can be measured by ultrasound or optical biometry before surgery.

Two families of method are used. Contact or immersion ultrasound A-scans have long been standard. Biometry based on PCI was done by the IOL Master, which is a light-based optical method. The methods do not give identical results. In one Toronto series, applanation and immersion ultrasound yielded significantly lower AL values compared to optical biometry measurements. Precision matters because an error of 1 mm will lead to a 2.5 D change in IOL power in normal eyes, while it jumps to 3.75 D in small eyes with axial length <20 mm. Errors in ultrasound axial length measurement have been held responsible for almost half of the errors in intraocular lens power calculation using ultrasound biometry. Optical methods reduced this source of error. One account notes that the influence of the error of axial length measurement on the refractive error decreased from over 50% (when measured with applanation ultrasound) to 36%. Optical biometry also placed a significantly larger percentage of cases within ± 0.50D of refractive error compared to ultrasound biometry in that series.

Each method has limits. Dense or posterior subcapsular cataracts diminish data quality, which can be quantified as signal-to-noise (SNR). Where SNR exceeds 2, the two methods show a minimum difference between optical and ultrasound biometry. Ultrasound retains a role in dense cataracts, pediatric cataracts, eyes filled with silicone oil, and uncooperative patients. Optical partial coherence interferometry is considered advantageous in highly myopic or staphylomatous eyes, where an ultrasound probe can struggle to measure the true axial length along the visual axis.

Congenital and Pediatric Cataract

Frequency and causes

Congenital cataract is one of the most important treatable causes of visual impairment in childhood. The worldwide incidence of congenital cataracts is unknown and likely underestimated in underdeveloped countries. Causes include inherited mutations affecting lens development, intrauterine infections such as rubella, and metabolic disorders, although many cases have no identifiable cause. Congenital cataract also occurs as part of multisystem conditions such as Down syndrome, galactosaemia and Lowe syndrome. The genetic and infectious pathways are discussed in the section on genetic and infectious causes.

Why timing matters

A lens opacity that blocks light during the early visual sensitive period can cause deprivation amblyopia, a loss of acuity in the affected eye that does not reverse with correction of the optics alone. To limit the severity of deprivation amblyopia, it is recommended that unilateral congenital cataracts be removed by 6 weeks of age and bilateral congenital cataracts be removed by 10 weeks of age. A 2025 meta-analysis of 28 studies, covering 2,167 patients, found that the pooled amblyopia prevalence was 62%, which indicates how often visual outcomes remain poor even after surgery. Earlier operations reduced amblyopia, but the same analysis reported that early surgery significantly reduced amblyopia risk but increased complications, notably glaucoma (26% vs. 6%). The trade-off between visual benefit and glaucoma risk is therefore central to timing decisions. Laterality also matters: unilateral partial obstruction conferred a higher amblyopia prevalence than bilateral complete obstruction (68% vs. 36%). One older series estimated that acuity fell by about one line for each three-week delay within the first 14 weeks of life. Prolonged amblyopia therapy beyond 6 years of age showed limited efficacy.

Surgery and the intraocular lens debate

Cataract surgery is the treatment of choice for visually significant congenital cataracts. After removal, the child still requires optical correction. For patients who are left without an intraocular lens (aphakic), appropriate correction of the refractive error either with contact lenses or aphakic glasses is necessary. In unilateral cases, patching of the better seeing eye is needed to manage the resulting amblyopia.

Whether to implant a lens at the time of surgery remains contested. Substantial debate still exists among paediatric ophthalmologists regarding the best practice of intraocular lens implantation in children. The Infant Aphakia Treatment Study, a randomized trial of 114 infants with unilateral congenital cataract, compared primary lens implantation with contact lens correction. Its long-term results showed that implanting an IOL at the time of cataract extraction was neither beneficial nor detrimental to the visual outcome. However, there were significantly more adverse events and additional intraoperative procedures in the IOL group. Costs also differed: one analysis found the mean cost of treatment for a unilateral congenital cataract with primary IOL implantation was $14 752 versus $10 726 with contact lens correction. For bilateral cases, one review concluded that the use of contact lenses for the correction of bilateral aphakia in children is the most practical approach, while acknowledging that lens implantation may be the only option in selected cases. Surgeons who do implant primary lenses in infants have also emphasised technique: one report of the youngest age group noted a substantial higher incidence of visual axis opacification in the eyes operated with implantation of an IOL (40% and 39%, respectively) compared with those who were left aphakic and treated with contact lenses (4% and 12%, respectively). The same authors favoured a bag-in-the-lens technique when primary implantation is chosen.

Glaucoma and long-term follow-up

Glaucoma associated with aphakia and pseudophakia is one of the most common complications of surgery for congenital cataract. Reported rates vary widely. One review noted that glaucoma ranges from 0% to 32% across series, and that the incidence of aphakic glaucoma also seems to increase with longer follow-up. Risk factors include surgery in the first year of life, microcornea (corneal diameter less than 10 mm), other ocular abnormalities, certain types of cataract, and a history of secondary membrane surgery. Diagnosis is difficult because diagnosis relies on clinical signs, such as elevated intraocular pressure (IOP) and optic nerve head cupping, as children are often unable to perform a visual field examination. Glaucoma may also appear late. In one series, it can be detected even years after cataract surgery (range 0.3-94 months), so long-term careful follow-up is necessary. Half of the affected eyes in that series needed surgical treatment, so the disease is clinically serious.

Visual rehabilitation after infant surgery is therefore prolonged. Visual rehabilitation requires many years of refractive correction (with contact lenses or aphakic glasses), possible patching for amblyopia, possible strabismus surgery, and glaucoma screenings. Management of glaucoma and related complications is thus a long-term component of paediatric cataract care rather than a one-time event.

Nonsurgical Management and the Evidence on Prevention

Temporary measures while awaiting surgery

Spectacles can offset part of the blur, but they leave the opacity itself untouched: Eyeglasses may help temporarily, but they do not address the underlying lens clouding. Because clouding also lowers contrast, people often need more light for close work, and they may also find they are more reliant on bright lighting compared to before. Magnifiers and adjusted task lighting therefore serve as stopgaps that improve how a clouded lens is used, without restoring its clarity.

Modifiable factors studied in relation to progression

Research has asked whether lifestyle and metabolic factors speed or slow lens clouding. Investigators have linked tobacco use, poor nutrition and diabetes to faster progression, and Smoking, poor nutrition, and systemic diseases such as diabetes are associated factors that can speed progression. Diabetes is especially relevant because elevated blood glucose is the mechanism through which diabetes is thought to act on the lens, so glycaemic control is studied as a possible brake on decline. Ultraviolet exposure is treated in the same way, with protective eyewear recommended as a precaution. Much of this evidence is observational, so these factors are better understood as associations than as proven means of slowing cataract.

Antioxidant supplement trials

Because oxidative damage is central to lens ageing, antioxidant supplements were tested directly. The National Eye Institute's Age-Related Eye Disease Study tested in randomized trials the effects of daily doses of zinc (80 mg) and an antioxidant combination of vitamin E (400 IU), vitamin C (500 mg), and betacarotene (15 mg) on the progression of AMD, and the effect of the antioxidant combination on the development and progression of lens opacities. Observational work had suggested protection, but these studies yielded inconsistent results. A Cochrane review found that, the trials provided no evidence of effect of the antioxidant vitamins beta‐carotene, vitamin E and vitamin C given alone or in combination on the incidence of cataract, its extraction or progression and on the loss of visual acuity. The doses used were also higher than the recommended daily allowances. One subgroup finding stands out: in a meta-analysis, beta-carotene's effect was not in favor of beta carotene except among current smokers. The reviewers do not recommend any further studies to examine the role of antioxidant vitamins beta‐carotene, vitamin C and vitamin E in preventing or slowing the progression of age‐related cataract. Taken together, supplementation has not been established as a preventive therapy.

Why no drug is approved to dissolve or reverse cataract

No medicine has been approved to clear an established opacity. There are no FDA-approved eye drops that can treat cataracts. The most discussed candidate is lanosterol, a sterol from the cholesterol pathway. Previous research had shown that lanosterol, which belongs to a group of chemical compounds called sterols, reversed cataracts. However, lanosterol was not water-soluble enough to be included in an eye drop solution and had to be injected into the eye. Its human use remains unproven: it hasn't been directly tested on humans yet, so researchers are still trying to find out if it's safe and effective. Older claims for N-acetylcarnosine drops have also not held up; a Cochrane review through 2016 reported "no convincing evidence that NAC reverses cataract, nor prevents progression of cataract".

The difficulty of delivery is rooted in lens anatomy. The lens lies deep behind the iris and receives no blood supply, so any agent must reach it through the cornea and the aqueous humour, or cross the blood–aqueous barrier after systemic dosing. Topical drops are partly cleared by tears and blinking, and only a small fraction penetrates the cornea. Systemic drugs face the same barrier, so effective concentrations in the lens are hard to achieve without high systemic exposure. These constraints, rather than a lack of biological targets, explain much of why no drug has reached widespread clinical use.

Indications and Timing of Surgery

Cataract extraction is usually a planned procedure, and the decision to operate depends on how far the opacity disrupts a person's function rather than on whether a cataract is visible on examination. Clinical guidance has moved away from fixed thresholds. The European Society of Cataract and Refractive Surgeons (ESCRS) bases indications on visual acuity and function, subjective visual disability, and expected benefit, without prescribing numerical cut-offs. The Royal Australian and New Zealand College of Ophthalmologists (RANZCO) states that no visual acuity level by itself makes surgery indicated or contraindicated. Some health systems still apply numerical rules for access. In Ethiopia, for example, indications include visual impairment, defined as acuity below 3/60, or vision that interferes with daily activities. The gap between clinical and administrative criteria can therefore affect who is operated on and when.

Functional impairment and daily life

The central question is which activities the cataract now limits. Commonly cited tasks include reading, particularly fine print or in dim lighting, recognising faces, watching television, safe mobility such as navigating stairs, driving particularly at night, and work requiring visual precision. Intermediate distances matter too: a study of cataract patients found that most of their time was spent on near and intermediate visual tasks, which means that a good distance acuity alone does not capture functional loss. The Australian Cataract Clinical Care Standard also treats disabling glare or contrast sensitivity loss as grounds for surgery even when best-corrected acuity is reasonable. Symptoms such as halos and glare around lights at night, colour yellowing, double vision in one eye, and frequent eyeglass prescription changes are typical signs that the lens is affecting function. Stronger spectacles or better lighting can help for a time, but these measures only provide temporary relief.

Some occupations raise the threshold for operating earlier. Surgeons have noted that the profession requires high visual precision (driver, pilot, surgeon, artist), and a decision may be brought forward on that basis even when everyday vision is still adequate.

Coexisting eye disease

Before surgery, clinicians check for other conditions that can limit the benefit or change the operation. Diabetic retinopathy and lens-induced angle-closure glaucoma are among the recognised medical indications in some guidance. A retinal pathology that requires a clean fundus examination can make an earlier operation desirable, because the clouded lens blocks the view of the retina. Glaucoma is a similar case: combined surgery can help control intraocular pressure. Delay carries its own risks. One clinical overview notes that delays can raise the risks of falls and lens-induced glaucoma or inflammation, and make it harder to check or treat the retina. Pre-operative assessment therefore weighs the likely gain in vision against the state of the retina, optic nerve and anterior segment.

Why surgery is the accepted treatment

Surgery is considered the only effective and widely accepted treatment for established cataract because no alternative has been shown to work in humans. There is currently no eye drop, supplement or medication proven to remove or reverse cataracts. Surgery remains the only effective treatment. Experimental work has not changed this position. Lanosterol-based eye drops produced partial recovery of lens transparency in rabbits and dogs, but the compound has not been shown to be effective in human clinical trials. Prevention is also unproven: there are no effective methods for cataract prevention or drug treatment at present. Surgery is therefore the reference point against which other approaches are judged, and the timing question is about when, not whether, to operate.

Factors that influence timing

Timing is shaped by several practical and clinical factors. Driving, especially at night, is one of the most frequent triggers. Fall risk is also discussed, but the evidence is mixed. A large study of Medicare beneficiaries found that cataract surgery was not associated with a significant difference in the risk of falls or fractures over one year. An Australian study, by contrast, reported that surgery actually increased the risk of falls, doubling the risk after first eye cataract surgery. A systematic review also noted a transitional period of increased vulnerability between the surgery of the first and second eye, with a temporary increase in the risk of falls and hospitalisations. Because of this, the decision about which eye to operate first and when to operate on the second is a timing question in its own right. Patient priorities, such as work demands, independence and the ability to attend follow-up visits, complete the picture.

Surgical Techniques

From couching to extraction

For centuries the usual treatment was couching (couching), which did not remove the clouded lens. It was practised across Central Asia, the Middle East, and Europe until the 1747 introduction of extracapsular extraction. The results were unreliable: 33.3% of patients who undergo traditional couching end up with no light perception vision.

Credit for the first planned extraction is generally given to the French surgeon Jacques Daviel. He performed the first such procedure in 1747, using an extracapsular technique, but did not present this case until 1752. His wound was made at the inferior limbus with a small knife and then enlarged with curved scissors, and a small spatula was used to 'detach' the cataract and remove it in pieces. In the extracapsular approach, the back (posterior) portion of the lens capsule is allowed to remain in the eye. That retained capsule later supports an implanted lens.

Phacoemulsification

The American ophthalmologist Charles Kelman published a preliminary report on phacoemulsification in 1967, in the American Journal of Ophthalmology. The idea reportedly came from an ultrasonic dental instrument. Ultrasonic probes for removing tartar were relatively new at the time. The first two phacoemulsifications in human patients took place between April and June of 1967, although exact dates are not known. In the procedure, the tip vibrates at high frequency to break the nucleus into fragments, which are then suctioned away through an incision of about 3 mm. Many ophthalmologists regarded the method as a radical departure from convention, and acceptance was slow. Today, it stands as the standard of care for cataract surgery in developed countries.

Manual small-incision surgery

Manual small-incision cataract surgery (MSICS) removes the lens through a small wound without an ultrasound unit, which matters where equipment is scarce. The contemporary MSICS technique most commonly employed is based on the method that Ruit et al first described in 1999. The description came from their experience at Tilganga Eye Centre in Kathmandu, Nepal. The surgeon creates a tunnel in the sclera and cornea and delivers the nucleus through it rather than emulsifying it. The external wound is a sutureless external incision of 6 mm to 7 mm that is enlarged to 10 mm internally with a keratome.

In a 2007 trial, Dr. Ruit and colleagues randomly assigned 108 outreach patients in Nepal with significant cataracts to receive either phacoemulsification or SICS. Both techniques had excellent surgical outcomes and similar uncorrected visual acuity on day 1 post-op. Cost is a central argument for the manual approach: manual small-incision cataract surgery costs 1,200 Nepalese rupees per eye (less than US $10), which is approximately 10% of the monthly minimum wage in both Nepal and the neighbouring Indian state of Bihar.

Femtosecond laser and robotic systems

Femtosecond laser platforms automate some steps of the operation, such as corneal incisions and capsule opening, and robotic or computer-assisted systems aim to improve precision and alignment. Whether these additions improve visual or safety outcomes beyond conventional phacoemulsification is still being compared in trials and cost analyses, and the evidence has not yet settled the question.

Intraocular Lenses

The first intraocular lens (IOL) was implanted by Harold Ridley on 29 November 1949 at St Thomas' Hospital in London. Ridley drew inspiration from the injuries of World War II pilots, and the lens was made from Perspex CQ, a form of polymethyl methacrylate (PMMA). It was placed in the posterior chamber after extracapsular cataract extraction. Before this, surgeons treated cataracts by removing the natural lens, and patients then wore thick lenses, often called "Coke bottle glasses," that helped with reading but distorted vision when walking. Ridley's method faced considerable skepticism and resistance from the medical community throughout the 1950s and 60s, and by the late 1970s IOLs had become an accepted option for correcting aphakia. Later designs moved away from rigid PMMA toward foldable silicone and acrylic materials, which allowed smaller incisions and gentler implantation. Design development since then has focused on three goals: correcting focus at more distances, correcting astigmatism, and allowing refinement after healing.

Most lenses implanted today are monofocal, meaning they are set to a single focal distance, usually distance vision. Traditional monofocal IOLs primarily restore distance vision, leaving patients reliant on spectacles for near and intermediate tasks. Patients who want to read without glasses therefore need reading spectacles after surgery unless a more complex lens is chosen.

Multifocal lenses divide incoming light between several focal points so that the eye can form usable images at more than one distance. This division is also the source of their drawbacks. The greater division of light that occurs as it passes through a trifocal IOL is responsible for optical phenomena such as glare and halos, and for a loss of contrast sensitivity. Trifocal designs give better near spectacle independence, but a meta-analysis of trifocal and hybrid multifocal-extended depth of focus lenses found that the halo photic effect was generated more frequently by the trifocal IOLs, while contrast sensitivity was broadly comparable between the groups. Extended depth of focus (EDOF) lenses were introduced to provide a useful range of vision with fewer photic side effects, and for patients for whom intermediate visual acuity is more important, EDOF IOLs might be the better choice. Findings on contrast sensitivity are not uniform: an American Academy of Ophthalmology report found that all patients who had multifocal and EDOF lenses implanted showed decreased contrast sensitivity and reported more visual phenomena as compared with control participants who received monofocal lenses, whereas a Bayesian network meta-analysis found no statistical differences between multifocal and monofocal IOLs regarding contrast sensitivity, glare, or halos. The choice therefore involves weighing near reading ability against the risk of visual disturbance, and it depends on a patient's occupation, night driving and expectations.

Toric lenses correct the corneal astigmatism that monofocal lenses leave uncorrected. They have a cylindrical power built into the optic and must be oriented precisely. Axis alignment is a practical constraint: these IOLs are available in only a few toric powers and the axis must be precisely aligned at surgery, and other than surgical repositioning there is no option to adjust the IOL's axis which may shift post-operatively. Healing can also change the astigmatism after the operation, which is why postoperative adjustment is attractive. Light-adjustable lenses (LAL) address this. The LAL is a photosensitive silicone intraocular lens whose power can be adjusted post-operatively using UV light at 365 nm. Over a 12 hour period, the remaining unexposed macromers physically diffuse into the exposed area, which changes the lens curvature and refractive power in a predictable way. The device was approved by the FDA for human use on 22 November 2017, and the lens is indicated for patients with corneal astigmatism of at least 0.75 D and no significant eye disease. A 2026 power-vector analysis suggested that the LAL advantage over toric lenses is largely the penalty for axis misalignment, and that below about 2 D on a stable platform, the gain was generally smaller than 0.50 D, so the benefit is greatest at higher cylinder and greater alignment uncertainty.

Across all these types, the main trade-offs concern optical quality against spectacle independence. Some lens types also carry demands on surgical planning, including accurate biometry and the need for an intact capsular bag. Their use in routine practice depends on cost, which is discussed elsewhere in this entry.

Complications and Postoperative Care

Most cataract operations are uneventful, but several complications are recognised, and some appear months or years after surgery. The most common delayed problem is posterior capsule opacification (PCO). Because the capsular bag is usually kept to hold the intraocular lens, residual lens epithelial cells can keep dividing and migrating across the posterior capsule, where they form opaque membranes. Reported incidence varies by population and definition: one review gives a range of about 3% to 50% within five years, and several series report roughly 20% at two years and about 28% at five years. PCO causes blurring, reduced contrast sensitivity and glare. Its standard treatment is a neodymium-doped yttrium aluminium garnet (Nd:YAG laser) capsulotomy, a brief outpatient procedure that opens the centre of the posterior capsule. Surgical capsulotomy is rarely needed, and the laser is not available in many low-income settings, where PCO is a larger burden.

The laser procedure has its own risks. Intraocular pressure usually rises within hours, peaks at about three to four hours and generally returns to baseline within a week, though in a minority of eyes the rise is prolonged enough to need glaucoma treatment. Cystoid macular oedema, retinal detachment, iritis and displacement of the lens implant are also described, and using less total laser energy and smaller openings is the usual way to reduce these risks.

Several complications threaten sight more directly. Endophthalmitis, an intraocular infection, is rare: published rates are commonly 0.1 to 0.5 per 1,000 operations, and a large US registry analysis reported 0.04% among patients aged 44 and over. Intraoperative posterior capsule rupture is among the strongest risk factors, with one case-control study estimating a nearly fourfold increase. Low surgical volume and the omission of antiseptic irrigation or intracameral antibiotics are also associated with infection, and intracameral antibiotics have been shown to work better than topical antibiotics alone. Cystoid macular oedema (pseudophakic CME, also called Irvine-Gass syndrome) is a leading cause of visual loss after surgery. A systematic review of 143 studies found a pooled cumulative incidence of about 5%. Its pathogenesis is considered multifactorial, and inflammation is thought to play a major role. Retinal detachment is less frequent: a Western Australian series of about 130,000 operations reported an overall rate near 0.7%, and a French cohort found a higher rate after extracapsular extraction than after phacoemulsification. Posterior capsule rupture, high myopia, male sex and younger age all raise the risk of detachment.

Postoperative inflammation is expected to some degree, because surgery disrupts the blood-aqueous barrier. It is usually managed with topical corticosteroids and non-steroidal anti-inflammatory drugs, and some surgeons add injected anti-inflammatory agents at the end of the operation. Pain is generally mild and is controlled with analgesics and the topical regimen. Long-term anti-inflammatory treatment, more frequent visits, optical coherence tomography monitoring and modified surgical technique are used for high-risk patients, and the ESCRS PREMED study, which enrolled more than 1,000 patients, informs prevention guidance for both diabetic and non-diabetic patients.

Several factors raise the overall risk of complications. Diabetes is the most consistently cited: it roughly triples the relative risk of CME, and the risk rises with the duration of diabetes, the severity of retinopathy and HbA1c levels, and diabetic eyes also face higher rates of PCO and endophthalmitis. A dense, hard nucleus demands more ultrasound energy and longer phacoemulsification time, which is associated with greater stress on the corneal endothelium and the macula. Limited surgical experience matters too: in a comparison of trainee and experienced surgeons, the trainee group had a markedly higher adjusted risk of retinal detachment. Uveitis, epiretinal membrane, retinal vein occlusion and prior vitrectomy are additional risk factors for CME.

Global Access, Surgical Rates, and Public Health Programmes

Measuring access: surgical rates and effective coverage

Planners often start with the cataract surgical rate (CSR), which divides the yearly number of operations by population size and scales the result to one million people; one review describes it as a proxy for access to cataract services in a country. Because a high operation count can mask unmet need, the field also tracks effective cataract surgical coverage (eCSC), which counts only people who had surgery and achieved a good visual result, divided by everyone who needed surgery as a proportion of all people who had received or were still to receive surgery.

National CSRs vary enormously. One review reports values from 36 to 12 800 per million population. Estimates for wealthy countries also differ by source: a clinic-published overview gives more than 5,000 per million each year, while an earlier review places them between 4,000 and 10,000 in economically developed countries. The WHO has used a benchmark of 3,000 per million as the minimum needed to eliminate cataract blindness greatly exceeded in many developed countries.

A 2026 analysis in The Lancet Global Health drew on 233 population-based surveys from 68 countries, covering 779,706 adults aged 50 years and older. It estimated global eCSC at 48.2% in 2025, rising to 52.3% by 2030. Coverage is lowest in Africa, where the regional median eCSC was 23.6% in 2025, and eCSC varies widely across countries, from just over 2% in some settings to nearly 78% in others. Men register higher eCSC than women across most WHO regions in most WHO regions. Low- and middle-income countries hold more than nine in ten of the 15.2 million people estimated to be blind from cataract in 2020 over 90% of these individuals live in low-income and middle-income countries.

Barriers to access in low- and middle-income countries

Obstacles operate on both the supply and demand sides. A shortage of health workers and surgical capacity drives long waiting times insufficient relevant health-care workers and surgical spaces driving long wait times for treatment. On the demand side, patients may avoid surgery out of fear, cost, or doubts about results, and surgeon shortages are most acute in Africa low demand because of fear of surgery. Reducing patient-incurred costs and expanding the workforce are identified as key priorities Key areas for prioritisation include increasing the size and expertise of relevant workforces and reducing patient-incurred costs. A Kenyan dynamic model estimated that, at current capacity, 77% of individuals on Kenya's cataract backlog in 2025 will die before receiving surgery, which is a modelled rather than observed figure.

Global programmes and national targets

The modern framework began with VISION 2020, launched in 1999 by the WHO and the International Agency for the Prevention of Blindness to eliminate avoidable blindness by 2020. The World Health Assembly later endorsed the Universal Eye Health global action plan, which in 2013 set a target to reduce the prevalence of avoidable blindness and visual impairment by 25% from the baseline of 2010, with cataract as the priority. The plan adopted CSR and cataract surgical coverage as measurable indicators cataract surgical rate (CSR – number of cataract surgeries performed per year per one million population) and cataract surgical coverage. In 2021 the 74th World Health Assembly set new goals, including a 30% increase in effective cataract surgical coverage by 2030 a 30% increase in effective coverage of cataract surgical rate by 2030. Progress is measured largely through population-based surveys. Rapid assessment of avoidable blindness (RAAB) surveys supplied much of the data for the 2026 analysis including Rapid Assessment of Avoidable Blindness (RAAB) data.

National implementation has been uneven. In a review of 28 national eye-care plans, 18 countries (64%) had set targets for the cataract surgical rate in their plan, yet only one country had set a target for cataract surgical coverage for future monitoring. The same analysis found that most of the 2030 targets were not on track: the projected increase of 8.4 percentage points between 2020 and 2030 far below the 30-point global target.

Task-sharing, training, and nongovernmental capacity

Expanding surgical capacity has increasingly relied on task-sharing, in which trained non-physician staff or mid-level workers take on screening, pre-operative assessment, and selected parts of the pathway, while ophthalmologists focus on operating. Training programmes, outreach camps, and hospitals run by nongovernmental organisations have been used to reach patients outside urban centres. Such models raise questions of quality: in many settings efficient coverage is lower than simple coverage, highlighting concerns about surgical quality, so monitoring outcomes is treated as part of expansion rather than a separate task.

Economic and Social Consequences

Cataract has economic effects through lost work, out-of-pocket spending and the time that relatives spend on care. The WHO puts the annual global productivity loss from vision impairment at about US$ 411 billion purchasing power parity. In 2020, among people aged 50 and over, cataract caused 45.5% of blindness cases and 38.9% of moderate and severe visual impairment. Employment falls with the degree of visual loss. One set of estimates gives reductions of 33.8%, 31.4%, and 8.9% for blindness, severe vision loss, and moderate vision loss, respectively.

Households and caregivers

In low-income settings, families often pay directly for surgery. In a survey of rural China, out-of-pocket surgical costs averaged RMB 2945 after reimbursement, and total out-of-pocket costs equalled 25.1% of annual household income. Some low-income patients need to borrow or sell assets to cover costs. Insurance coverage and registration as a poverty-stricken household both reduced this burden in the same study. Surgery costs in rural areas have been reported to exceed annual disposable income.

The cost of informal care is often larger than the patient's own loss. In a health-economic model built for a low-income country, 68% of costs were the opportunity cost of the caregiver, because the patient would be blind for 12 years. The WHO also notes that the share of vision impairment caused by untreated cataract is higher in low- and middle-income countries than in high-income countries .

Function, falls and mental health in older adults

A six-year longitudinal study in Bangladesh and the Philippines compared people with cataract-related visual impairment with unaffected controls. One year after surgery, participation and time in productive activities, per capita expenditure and quality of life rose significantly, and the operated group became similar to controls. These gains were still present after six years, although time spent on productive activities fell in both groups.

Falls are another route to loss of independence. Vision impairment increases the risk of falls and related injuries in older adults. Among people awaiting surgery in one study, 30.7% had fallen while waiting for cataract surgery. The evidence on surgery itself is not uniform: one review reports that cataract surgery has been shown to reduce the incidence of falls, whereas a Medicare-based analysis estimated a reduction of -0.32 percentage points, with a confidence interval that did not reach significance.

Depressive symptoms show a similar pattern of association with mixed causal evidence. A community survey of about 4,600 older adults in one Chinese town found that the link between cataracts and depression is independent of other factors, and appears strongest among older adults with lower education. Whether surgery reduces depression is still debated, since several studies have demonstrated favorable effects on anxiety or depression, while others have found no significant effect. Reduced social participation and dependence on others are among the proposed mechanisms.

Cost-effectiveness and policy debate

Surgery is among the most frequently cited examples of an efficient health intervention, although estimates vary widely. An early estimate placed cost per disability-adjusted life year (DALY) averted at 730 to 2400 international dollars for "developed countries", against 90 to 370 international dollars for "developing countries". A later analysis of a Nepal programme reported a cost of US$ 5.06 per disability-adjusted life year (DALY) under its best-estimate scenario. Analyses that use a threshold of one times GDP per capita per DALY would classify most of these figures as cost-effective.

The economic result depends on the age at operation. For patients with mild or moderate impairment, one model found it to be cost-saving to perform the surgery before the age of 65; for patients with severe impairment it is cost-saving to operate until age 78. Critics argue that earlier analyses did not adequately address the composition of costs or the relevance of the patient's age. Wider economic arguments also turn on the scale of losses: one analysis found that 31 countries experience losses exceeding 1.2% of GNI, including 12 in Sub-Saharan Africa.

Differences across social groups

Access and burden are unevenly distributed. Women are at higher risk for cataract and are less likely to receive sight-restoring surgery. Rural residents, the poor and people with less schooling face the greatest financial and informational barriers, which is why the economic consequences of cataract fall most heavily on low-income households and on those with the least financial protection.

History and Terminology

Couching is the oldest documented treatment for cataract. In it, a needle or pointed instrument pushed the clouded lens out of the line of vision, usually toward the back of the eye, rather than removing it. The earliest written accounts are usually linked to Sushruta Samhita, an Indian medical treatise. Its date is disputed: sources give figures ranging from about 800 BCE to about 600 BCE, and some traditions attribute the Uttara Tantra section to Nagarjuna in the early Common Era. Other early evidence includes the Code of Hammurabi, which refers to eye surgery with a bronze lancet, and a wooden statue from the Fifth Dynasty of ancient Egypt (about 2457–2467 BCE) whose pupil bears a white patch thought to represent a cataract. In Europe, the Greek philosopher Chrysippus of Soli is cited as an early source, and Latin writer Celsus described couching in De Medicina in the first century BCE. Couching spread along trade routes and remained the principal method for many centuries. It was largely abandoned in favour of lens removal in the eighteenth and nineteenth centuries, and by 1753 Samuel Sharp had recorded the removal of the entire lens and its capsule. Couching still survives in some remote settings in parts of Africa and Asia.

Ancient physicians did not place the opacity inside the lens. Writers in antiquity generally believed the clouding lay in front of the lens, and terms such as the Latin suffusio ("spreading out") reflected the idea of an abnormal humour flowing into the eye. Within Islamic medicine, Ibn al-Haytham's Book of Optics, composed between about 1011 and 1021, gave the first systematic description of the eye's parts, including the cornea, aqueous humour, lens and vitreous, and it rejected the older extramission theory in favour of the view that light enters the eye from objects. Its Latin translation in the twelfth century made it influential in medieval Europe, and Roger Bacon later reaffirmed its findings. Understanding of the lens as a light-focusing structure, however, developed mainly through optics rather than through pathology. Medieval and early modern anatomists refined the description of the eye, but the idea that a cataract is an opacity of the lens itself became standard only as dissection and surgical experience accumulated.

The English word derives from Latin cataracta, meaning "waterfall" or "portcullis", which in turn comes from the Greek katarrhaktēs, "downrushing", from katarassein, "to dash down". The English medical sense, "opacity of the lens", is first recorded in the fourteenth or fifteenth century. Dictionaries offer somewhat different dates, and the link to the portcullis is commonly explained as a comparison: the clouding obstructs sight as a falling grating blocks a passage. The Chinese term 白内障 combines 白, "white", with 内障, a classical category of eye disorder located inside the eye, as opposed to external ones. The same characters are used in Japanese for the eye disease. The Chinese name is therefore descriptive, while the English name is metaphorical. The historical details of how 白内障 was adopted in modern Chinese medical usage are not covered here.

Terminology and classification changed considerably from the nineteenth century onward. Couching, which had been the standard procedure for centuries, was replaced by extraction, and the cataract came to be defined by the anatomical site of its opacity: nuclear, cortical or posterior subcapsular. The shift from describing the condition in terms of humours and obstructions to describing it as a lens disorder reflected the wider transformation of medicine during the scientific revolution and later, as clinical observation and pathology became central to ophthalmology.

Research Frontiers and Emerging Technologies

Research on cataract is moving in several directions, but none has yet produced a non-surgical treatment that matches surgery. The most visible line of work concerns drugs that might loosen protein aggregates inside the lens. Lanosterol, a compound that is abundant in the lens, has drawn the most attention. Preclinical work reported that a lanosterol-derived compound improved antioxidant activity and reduced lens opacity by inhibiting protein aggregation In preclinical work, ZOC2017217 improved antioxidant activity and reduced lens opacity by inhibiting protein aggregation associated with cataract formation. Other experiments have been less favourable. In cultured rat lenses, lanosterol liposomes failed to either reverse these lens opacities or prevent the further progression of cataracts to the nuclear stage. A laboratory study on human lens material likewise found lanosterol failed to dissolve aggregated proteins or restore clarity in cultured human cataractous lens nuclei. A placebo-controlled pilot trial of the lanosterol-derived drop ZOC2017217 was started in February 2026 as a multicenter, randomized, placebo-controlled U.S. study. Earlier Chinese exploratory data reported that 50–86% of treated participants reached 20/40 vision or better within a few months, but these results await confirmation under stricter conditions. Commercially sold lanosterol products lack peer-reviewed studies backing their claims and fall outside strict regulatory oversight. No eye drop is FDA-approved to treat or reverse cataracts.

A central obstacle to any drug is reaching the lens at all. The lens has no blood supply and instead receives necessary nutrients and processes metabolites through aqueous and vitreous humor. Topical drugs must cross the tear film, the conjunctiva, and the blood-aqueous barrier, which is formed by tight junctions of the inner, non-pigmented epithelium of the ciliary body. Much of an eye-drop dose may also be lost to the systemic circulation through conjunctival absorption the high degree of vascularization results in significant drug loss into the body circulation and the posterior segment of the eye. Nanocarriers are being developed to address these problems. Their proposed advantages include enhancing drug permeability across the blood-aqueous barrier and cornea, prolonging drug contact time with ocular tissues, and protecting the drug from degradation. Other laboratory work has explored gold nanoparticles carrying an antioxidant compound for cataract prevention gold nanoparticles with N-acetylcarnosine stabilized with polyphenols were obtained. These approaches remain at the stage of preclinical testing, and the controlled human evidence needed to judge them is largely absent.

Regenerative approaches aim to rebuild the lens rather than replace it. Work on mammalian lens epithelial stem cells showed that Pax6 and Bmi1 are required for LEC renewal. Building on this, a 2016 study reported a surgical method that preserves endogenous LECs and achieves functional lens regrowth. In that trial, 12 infants and toddlers who had been born with cataracts in both eyes were treated, and all 24 eyes developed clear, healthy lenses within three months of the novel surgery. A comparison group of 25 infants received standard surgery The latter control group experienced a higher incidence of post-surgery inflammation. The regenerated lenses have limitations. Earlier work noted that the regenerated lens was opaque, and there remained a significant disparity between the regenerated lens and a natural lens in terms of shape, thickness, structure, optical property, and that this approach is not suitable for patients with gene-related congenital cataracts. Other groups have tried implanting cells derived from human embryonic stem cells into the lens capsule. In animal models, these cells formed a lens with the most transparent, thickest profile reported in that study. The field is still at the level of small early-stage trials and animal work.

Computational methods are being applied in two main areas. In biometry, artificial intelligence and machine learning models are being trained on large sets of measurements and surgical outcomes to improve intraocular lens power prediction, particularly in eyes with unusual dimensions. Deep learning systems are also being tested for detecting and grading lens opacity from photographs and slit-lamp images, which connects to diagnostic work. During surgery, image-analysis software is being studied to guide incisions and alignment. Evidence for these tools is still mostly retrospective or confined to single centres, and their added value over established formulas has not been settled. A separate group of commercial, non-invasive light-based devices claims to clear the lens or delay cataract. These devices generally lack peer-reviewed validation, and their claims should be weighed accordingly.

Unresolved Questions and Debates

Attributing age-related cataract to specific causes is difficult because the lens accumulates change over decades, and several exposures act on it at once. Ultraviolet light has a strong mechanistic basis, since it damages lens proteins and generates oxidative stress, but its share of the total burden is hard to isolate from age, occupation and outdoor lifestyle. Air pollution is linked to cataract in observational studies, yet it tends to co-vary with urbanization and income, so separating its direct effect from socioeconomic factors remains uncertain. Metabolic disease is more firmly established: diabetes is consistently associated with earlier and faster lens opacification, but researchers still debate how much of this risk depends on glycaemic control, disease duration, or the drugs used. Genetic studies have identified variants associated with cataract, but known variants explain only part of the variation in common age-related disease. Because these factors overlap, a single estimate of how much each one contributes is hard to defend.

A second debate concerns whether earlier surgery or new drugs could meaningfully reduce the number of people with cataract. Surgery does not prevent cataract from forming; it restores vision once opacity has reached a functional threshold. This means that operating earlier mainly changes when people are treated, while the number of new cases each year is unaffected. A drug that slowed lens opacification would act on incidence and could reduce prevalence over time, but no such agent has been approved, and antioxidant trials have not produced a clear preventive effect. Evaluating these options requires long follow-up and outcome measures that reflect visual function rather than lens appearance alone, which is why randomised trials and evidence-based comparisons of timing strategies are slow and costly to conduct.

Premium intraocular lenses, including multifocal, extended-depth-of-focus, toric and light-adjustable designs, raise a separate question about value. A review of premium versus standard lenses reported that premium options carried substantially higher direct costs, with one cost-effectiveness analysis giving figures of about $5,319 for multifocal lenses against about $1,928 for monofocal lenses, while clinical benefits favoured either lens type depending on the outcome measured. Premium lenses can reduce dependence on spectacles, but they may bring trade-offs in glare and contrast sensitivity. Where health systems fund surgery publicly, the question becomes whether scarce resources should support premium options for some patients or basic surgery for many more. This is a matter of economic judgement as much as clinical evidence, and the answer depends on how quality-of-life gains are weighed against cost.

The largest unresolved issue concerns the global surgical gap. Estimates from population-based surveys in 68 countries suggest that effective cataract surgical coverage stood at about 48.2% in 2025 and is projected to rise by only 8.4 percentage points between 2020 and 2030, far short of the 30-point target endorsed by the World Health Organization in 2021. Coverage in the WHO African region was estimated at 23.6% in 2025. Quality varies sharply as well: country-level figures ranged from about 2.1% in Burundi to about 77.7% in Qatar, and uncorrected refractive error was a major reason for poor outcomes. Strategies that prioritise volume, such as mobile outreach, primary-level screening, task-sharing and lower-cost manual techniques, can expand access quickly, but they must be paired with refraction services, training and outcome monitoring to avoid a larger population of operated eyes with poor vision. Deciding which approach best serves the largest unmet need, particularly among women and in low-income regions, is an ongoing policy question within the broader aims of universal-health-coverage and the sustainable-development-goals.

References

1. Homeostasis in the vertebrate lens: mechanisms of solute exchange - PMCpmc.ncbi.nlm.nih.gov
2. Association of Alpha-Crystallin with Fiber Cell Plasma Membrane of the Eye Lens Accompanied by Light Scattering and Cataract Formation - PMCpmc.ncbi.nlm.nih.gov
3. Lens Metabolism - an overviewsciencedirect.com
4. Lens Fiber - an overviewsciencedirect.com
5. Lens Protein - an overviewsciencedirect.com
6. Function and Aggregation in Structural Eye Lens Crystallinspubs.acs.org
7. Lens aging: Effects of crystallins - ScienceDirectsciencedirect.com
8. Cataractstore.aao.org
9. On the contribution of the nucleus and cortex to human lens shape and size - Augusteyn - 2018 - Clinical and Experimental Optometry - Wiley Online Libraryonlinelibrary.wiley.com
10. Lens Nucleus - an overviewsciencedirect.com
11. Lens Cortex - an overviewsciencedirect.com
12. Types of cataractsallaboutvision.com
13. What are the Three Types of Cataracts?eyecenteroftexas.com
14. The 3 Types Of Cataracts: Nuclear Sclerotic, Cortical ...southcaleye.com
15. What Are the 3 Types of Cataracts? Causes & Differences Explaineddayaleyecentre.in
16. Cataract Types: Understanding Nuclear, Cortical, and Subcapsular - Apple Eye Careappleeyecare.com
17. Clearing up canine cataracts - Oklahoma State Universitynews.okstate.edu
18. Canine cataractsvet.cornell.edu
19. Cataracts in Dogsvcahospitals.com
20. Cataract - Canineindyanimaleyeclinic.com
21. A retrospective-cohort study on the development of cataracts in dogs with diabetes mellitus: 200 cases - PubMedpubmed.ncbi.nlm.nih.gov
22. Hereditary cataract status in canines based on HSF4 gene markerimage-ppubs.uspto.gov
23. Diabetic Cataracts and Retinopathy in Dogs - Veterinary Vision Centerveterinaryvisioncenter.com
24. Protein Misfolding and Aggregation in Cataract Disease and Prospects for Prevention - PMCpmc.ncbi.nlm.nih.gov
25. Senile cataracts and oxidative stress - ScienceDirectsciencedirect.com
26. UV-B induced fibrillization of crystallin protein mixturesncbi.nlm.nih.gov
27. Age-related nuclear cataract—oxidation is the keyresearchgate.net
28. Protein Misfolding and Aggregation in Cataract Disease and Prospects for Preventionresearchgate.net
29. Spandidos Publications: Molecular Medicine Reportsspandidos-publications.com
30. An ultraviolet-driven rescue pathway for oxidative stress to eye lens protein human gamma-D crystallinncbi.nlm.nih.gov
31. Global, regional, and national burden of cataract among older adults from 1990 to 2021: a comprehensive analysis based on the global burden of disease study 2021ncbi.nlm.nih.gov
32. Frontiersfrontiersin.org
33. Global trends in cataract burden: a 30-year epidemiological analysis and prediction of 2050 from the Global Burden of Disease 2021 study - PMCpmc.ncbi.nlm.nih.gov
34. Global, regional, and national burden of cataract: A comprehensive analysis and projections from 1990 to 2021ncbi.nlm.nih.gov
35. (PDF) Global trends in cataract burden: a 30-year epidemiological analysis and prediction of 2050 from the Global Burden of Disease 2021 studyresearchgate.net
36. Cataractnutritionguide.pcrm.org
37. Changing Trends in the Global Burden of Cataract Over the Past 30 Years: Retrospective Data Analysis of the Global Burden of Disease Study 2019ncbi.nlm.nih.gov
38. Number of People Blind or Visually Impaired by Cataract Worldwide and in World Regions, 1990 to 2010iovs.arvojournals.org
39. Global estimates on the number of people blind or visually impaired by cataract: a meta-analysis from 2000 to 2020nature.com
40. Cataract Remains Leading Global Cause of Blindness - Prevent Blindnesspreventblindness.org
41. Changing patterns in global blindness: 1988–2008ncbi.nlm.nih.gov
42. Global Causes of Preventable Blindness and Vision Impairmenteyerounds.org
43. Global, Regional, and National Burden of Early-Onset Cataract from 1990 to 2021: Findings from the Global Burden of Disease Study 2021 - PubMedpubmed.ncbi.nlm.nih.gov
44. Nuclear cataract - American Academy of Ophthalmologyaao.org
45. Prevalence of myopic shifts among patients seeking cataract surgeryscielo.org.ar
46. Nuclear Cataract and Myopic Shift in Refractionresearchgate.net
47. Second Sight and Cataracts: Why Reading May Improvesmartvisionoptometry.com.au
48. Nuclear Sclerotic Cataractsspecialty.vision
49. Nuclear Cataract: Symptoms, Causes, and Treatment Optionscentreforsight.net
50. Understanding Nuclear Cataract: Causes, Symptoms, and Treatment - Zocvi Editorialzocvi.com
51. Cataracten.wikipedia.org
52. Why Cataracts Cause Faded Colors & Night Vision Problemscenterforsight.net
53. Having Trouble Seeing at Night? Cataracts Could Be Affecting Your Visionadvvisioncenters.com
54. Most Common Cataract Symptoms You Should Not Ignoreeyecareofsandiego.com
55. Basic Approach to Diplopia - EyeWikieyewiki.org
56. 5 Signs of Cataracts to Watch Foropticarevision.com
57. Cataract - Ophthalmology - Merck Manual Professional Editionmerckmanuals.com
58. Cataract Grading: Types, Chart, Stages, and Classificationcentreforsight.net
59. Grading cataracts - The Cataract Coursecataractcourse.com
60. How Doctors Grade Cataractsdragarwal.com
61. Evaluation of the relation between Lens Opacities Classification System III grading and nuclear size by direct measurement - PMCpmc.ncbi.nlm.nih.gov
62. The Lens Opacities Classification System IIIjamanetwork.com
63. (PDF) The Lens Opacities Classification System III. The Longitudinal Study of Cataract Study Groupresearchgate.net
64. The Lens Opacities Classification System III (1993)scispace.com
65. Evaluation of Lens Opacities Classification System III... : Optometry and Vision Sciencejournals.lww.com
66. The Lens Opacities Classification System III Grading in Irradiated Uveal Melanomas to Characterize Proton Therapy-Induced Cataracts - American Journal of Ophthalmologyajo.com
67. AI-based diagnosis of nuclear cataract from slit-lamp videosncbi.nlm.nih.gov
68. (PDF) Comparison of optical biometry versus ultrasound biometry in cases with borderline signal-to-noise ratioresearchgate.net
69. Ultrasound Biometry vs. IOL Master - Ophthalmologyaaojournal.org
70. Preoperative measurements for cataract surgery: a comparison of ultrasound and optical biometric deviceslink.springer.com
71. Ultrasound Biometry - StatPearls - NCBI Bookshelfncbi.nlm.nih.gov
72. Intraocular Lens Power Calculation Using Pre- and Intra-operative Measurementsclinicaltrials.gov
73. Intraocular lens power calculationen.wikipedia.org
74. Congenital Cataract: Background, Pathophysiology, Epidemiologyemedicine.medscape.com
75. Postoperative amblyopia in children with congenital cataracts: a systematic review and meta-analysisijponline.biomedcentral.com
76. Congenital Cataract Treatment & Management: Medical Care, Surgical Care, Consultationsemedicine.medscape.com
77. The outcomes of paediatric cataract surgery with intraocular lens insertion in sub-Saharan Africa: a systematic review - PMCpmc.ncbi.nlm.nih.gov
78. Long-term Effect of Intraocular Lens vs Contact Lens Correction on Visual Acuity After Cataract Surgery During Infancy: A Randomized Clinical Trialresearchgate.net
79. A Randomized Clinical Trial Comparing Contact Lens to Intraocular Lens Correction of Monocular Aphakia during Infancy: HOTV Optotype Acuity at Age 4.5 Years and Clinical Findings at Age 5 years - PMCpmc.ncbi.nlm.nih.gov
80. Cost of Intraocular Lens versus Contact Lens Treatment after Unilateral Congenital Cataract Surgery: Retrospective Analysis at Age 1 Year - ScienceDirectsciencedirect.com
81. Contact Lenses—The Most Practical though not the Only Solution in Bilateral Paediatric Cataract - ScienceDirectsciencedirect.com
82. Bag‐in‐the‐lens intraocular lens in paediatric cataract surgery: intraoperative and postoperative outcomes - Boonstra - 2022 - Acta Ophthalmologica - Wiley Online Libraryonlinelibrary.wiley.com
83. Aphakic and Pseudophakic Glaucoma After Congenital Cataract Surgery - American Academy of Ophthalmologyaao.org
84. Aphakic Glaucoma After Congenital Cataract Surgeryjamanetwork.com
85. Treatment results in aphakic patients with glaucoma following congenital cataract surgery - PubMedpubmed.ncbi.nlm.nih.gov
86. Effect of Timing of Initial Cataract Surgery, Compliance to Amblyopia Therapy on Outcomes of Secondary Intraocular Lens Implantation in Chinese Children: A Retrospective Case Seriesncbi.nlm.nih.gov
87. Can Cataracts Be Reversed? Myths & Treatment Optionsfloridaeyespecialists.com
88. What is Nuclear Sclerosis? - Eye Laser Specialistseyelaserspecialists.com.au
89. What Is Nuclear Sclerosis? Definition, Causes, Symptoms ❰ SHORT READS ❱lens.com
90. S0000B: Vitamin E and/or Selenium in Preventing Cataract and Age-Related Macular Degeneration in Men on SELECT SWOG-S0000cdn.clinicaltrials.gov
91. The Effect of Multivitamin/Mineral Supplements on Age-Related Cataracts: A Systematic Review and Meta-Analysisncbi.nlm.nih.gov
92. Antioxidant vitamin supplementation for preventing and slowing the progression of age‐related cataract - PMCpmc.ncbi.nlm.nih.gov
93. A Systematic Review and Meta-analysis on the Effectiveness of Antioxidant Vitamin and Mineral Supplements on the Development and Progression of Age Related Cataractiovs.arvojournals.org
94. Using Eye Drops for Cataract Treatmentallaboutvision.com
95. Could eye drops be an alternative treatment to cataract surgery?aoa.org
96. Acetylcarnosineen.wikipedia.org
97. Randomized Trials of Vitamin Supplements and Eye Diseaseclinicaltrials.gov
98. When Should You Consider Cataract Surgery? A Comprehensive Guide to Timing and Decision-Makingeyecataractretina.com
99. Assessment of cataract surgery outcomes at Jimma Medical Center, Jimma, Southwest Ethiopia - PMCpmc.ncbi.nlm.nih.gov
100. Editorial: Addressing the unmet needs of cataract patients: when quality of vision can make the difference in quality of lifencbi.nlm.nih.gov
101. When Is Cataract Surgery Recommended? Signs & Symptomseyesurgerytoday.com
102. When Is the Right Time to Consider Cataract Surgery? - Retina Eyeretina-eye.co.uk
103. When to operate on cataracts? Criteria, signs and what no one explains to youdralinowrouzi.com
104. Best Time for Cataract Surgerycentreforsight.net
105. Can You Get Rid Of Cataracts Without Surgery?berkeleyeye.com
106. Cataract: Advances in surgery and whether surgery remains the only treatment in future - ScienceDirectsciencedirect.com
107. The association of cataract surgery with risk of falls and fractures among Medicare enrollees with cataract - PubMedpubmed.ncbi.nlm.nih.gov
108. The association of cataract surgery with risk of falls and fractures among Medicare enrollees with cataract - PMCpmc.ncbi.nlm.nih.gov
109. Impact of Cataract Surgery on Postural Control and Fall Risk in Adults and the Elderly: A Systematic Reviewmdpi.com
110. Origins of the first extracapsular cataract extraction: the legacyeyemuseum.ranzco.edu
111. Advances in Cataract Surgery - Page 2medscape.com
112. Extracapsular cataract extraction in Europe prior to Jacques Daviel - Grzybowski - 2023 - Acta Ophthalmologica - Wiley Online Libraryonlinelibrary.wiley.com
113. Process for cataract extractionimage-ppubs.uspto.gov
114. 50 years of phacoemulsificationophthalmologymanagement.com
115. Phacoemulsification for outpatient cataract surgery - Lasker Foundationlaskerfoundation.org
116. (PDF) How Charles Kelman Invented Phacoemulsification in the 1960s: a Reappraisal.researchgate.net
117. (PDF) Charles Kelman: The Father of Phacoemulsificationresearchgate.net
118. Manual Small Incision Cataract Surgery - EyeWikieyewiki.org
119. Surgeon brings innovative techniques to ophthalmologists worldwidehealio.com
120. High-volume cataract surgery in Lahan, Nepalncbi.nlm.nih.gov
121. Charles Kelman: The Father of Phacoemulsificationncbi.nlm.nih.gov
122. Sir Harold Ridley as the Pioneer of Intraocular Lenses: His Inspiration Drawn From World War II Pilotsncbi.nlm.nih.gov
123. Intraocular Lens Innovations, Then and Nowhealthcare.utah.edu
124. Multifocal Intraocular Lenses and Extended Depth of Focus Intraocular Lensesresearchgate.net
125. Multifocal and extended depth of focus intraocular lenses - Kondylis - Annals of Eye Scienceaes.amegroups.org
126. Comparison of trifocal or hybrid multifocal-extended depth of focus intraocular lenses: a systematic review and meta-analysisncbi.nlm.nih.gov
127. Visual Outcomes and Optical Quality of Accommodative, Multifocal, Extended Depth-of-Focus, and Monofocal Intraocular Lenses in Presbyopia-Correcting Cataract Surgery: A Systematic Review and Bayesian Network Meta-analysisjamanetwork.com
128. Multifocal and Accommodating Intraocular Lenses for the Treatment of Presbyopia - Ophthalmologyaaojournal.org
129. Using the light adjustable lens (LAL) to increase the depth of focus by inducing targeted amounts of asphericityimage-ppubs.uspto.gov
130. Use of the light-adjustable lens to correct astigmatism after cataract surgeryauthors.library.caltech.edu
131. Light Adjustable Intraocular Lenses - EyeWikieyewiki.org
132. Residual Astigmatism With Toric Versus Light-Adjustable Intraocular Lenses: A Power-Vector Model of the Effect of Alignment Uncertainty - PubMedpubmed.ncbi.nlm.nih.gov
133. Harold Ridley and the invention of the intraocular lens - PubMedpubmed.ncbi.nlm.nih.gov
134. Intraocular lensimage-ppubs.uspto.gov
135. Refractive and visual outcomes of plate-haptic toric intraocular lens implantation for astigmatic correction after uncomplicated microincision cataract surgeryncbi.nlm.nih.gov
136. An Overview of Nd:YAG Laser Capsulotomyncbi.nlm.nih.gov
137. Interventions for preventing posterior capsule opacification - PMCpmc.ncbi.nlm.nih.gov
138. Optical coherence tomography for an in-vivo study of posterior-capsule-opacification types and their influence on the total-pulse energy required for Nd:YAG capsulotomy: a case seriesncbi.nlm.nih.gov
139. The effect of Nd:YAG laser treatment of posterior capsule opacification on anterior chamber depth and refraction in pseudophakic eyes - PMCpmc.ncbi.nlm.nih.gov
140. Nd:YAG Laser Posterior Capsulotomy - American Academy of Ophthalmologyaao.org
141. Visual Outcomes, Intraocular Pressure Changes, and Complications Following Nd:YAG (Neodymium-Doped Yttrium Aluminum Garnet) Laser Posterior Capsulotomy for Posterior Capsular Opacification: A Prospective Clinical Study - PMCpmc.ncbi.nlm.nih.gov
142. Cystoid Macula Edema Following Cataract Surgery - EyeWikieyewiki.org
143. Risk Factors and Cumulative Incidence of Cystoid Macular Edema After Simple Cataract Surgery: A Systematic Review and Meta-Analysis - PMCpmc.ncbi.nlm.nih.gov
144. Risk factors for and diagnosis of pseudophakic cystoid macular edema after cataract surgery in diabetic patients - PubMedpubmed.ncbi.nlm.nih.gov
145. Diabetes and Phacoemulsification Cataract Surgery: Difficulties, Risks and Potential Complicationsncbi.nlm.nih.gov
146. Common Risk of Cystoid Macular Edema after Cataract Surgeryrvaf.com
147. Incidence and Risk Factors for Retinal Detachment Following Cataract Surgery at a Tertiary Center in Jeddah, Saudi Arabiancbi.nlm.nih.gov
148. Incidence and risk factors for retinal detachment after cataract surgery: a comparison between trainee and experienced surgeonsncbi.nlm.nih.gov
149. Royal College of Ophthalmologists’ National Ophthalmology Database, Report 10: Risk Factors for Post–Cataract Surgery Endophthalmitis - Ophthalmologyaaojournal.org
150. Risk factors for endophthalmitis following cataract surgery: a retrospective case–control study - ScienceDirectsciencedirect.com
151. A Review of Postop Endophthalmitisreviewofophthalmology.com
152. The occurrence rate of acute-onset postoperative endophthalmitis after cataract surgery in Chinese small- and medium-scale departments of ophthalmologyncbi.nlm.nih.gov
153. Cataract Surgical Rate and Socioeconomics: A Global Studyiovs.arvojournals.org
154. Effective cataract surgical coverage in adults aged 50 years and older: empirical estimates from population-based surveys in 68 countries and modelled estimates for 2000–30 - The Lancet Global Healththelancet.com
155. Global prevalence of cataract surgery : Current Opinion in Ophthalmologyovid.com
156. Global Cataract Statistics 2025 (Worldwide Data)londoncataractcentre.co.uk
157. Rising Cataract Surgery Rates: Demand and Supply - Ophthalmologyaaojournal.org
158. Effective Cataract Surgical Coverage trends highlight gaps in cataract services towards 2030 targets - IAPB Vision Atlasvisionatlas.iapb.org
159. Barriers to accessing cataract surgery - The Lancet Healthy Longevitythelancet.com
160. Global cataract surgery coverage gains fall short of 2030 target, analysis finds - Ophthalmology 360ophthalmology360.com
161. Assessing the cataract surgical rate and gender equity in cataract services in south-east Nigeria - PMCpmc.ncbi.nlm.nih.gov
162. pmc.ncbi.nlm.nih.govpmc.ncbi.nlm.nih.gov
163. Nearly half of people facing cataract-related blindness still need surgerymedicalxpress.com
164. Eliminating cataract blindness: Are we on target? - PMCpmc.ncbi.nlm.nih.gov
165. Integrating primary eye care with primary health care: tracing the journey - PMCpmc.ncbi.nlm.nih.gov
166. Global Cataract Surgery Targets Unlikely to Be Met by 2030 - Ophthalmology Advisorophthalmologyadvisor.com
167. Evidence for national universal eye health plansncbi.nlm.nih.gov
168. Evidence for national universal eye health plans - PMC - NIHpmc.ncbi.nlm.nih.gov
169. Field testing project to pilot World Health Organization global eye health indicators in Latin America: lessons learned thus farncbi.nlm.nih.gov
170. Full article: WHO Vision 2020: Have We Done It?tandfonline.com
171. The Lancet Global Health Commission on Global Eye Healththelancet.com
172. Vision impairment and blindnesswho.int
173. Distributions and trends of the global risk-attributable cataract burden from 1990 to 2021 - ScienceDirectsciencedirect.com
174. Economic Impact of Vision Impairment: Cataract Awareness Monthhelpmesee.org
175. Out-of-pocket expenditure for cataract surgery in rural China: a cross-sectional survey combined with hospital administrative data - PMCpmc.ncbi.nlm.nih.gov
176. Cataract Surgery in Low-Income Countries: A Good Deal! - PMCpmc.ncbi.nlm.nih.gov
177. The Long Term Impact of Cataract Surgery on Quality of Life, Activities and Poverty: Results from a Six Year Longitudinal Study in Bangladesh and the Philippinesncbi.nlm.nih.gov
178. Cataract Surgery and Mental Health: A Comprehensive Review on Outcomes in the Elderly - PMCpmc.ncbi.nlm.nih.gov
179. Association of Visual Impairment and Falls in Elderly Individuals-A Cross-Sectional Study - PMCpmc.ncbi.nlm.nih.gov
180. Effect of cataract surgery on risk of falls or fractures in Medicare beneficiaries with cataractsacademic.oup.com
181. Cataracts Linked to Increased Odds of Depression in Older Adultswolterskluwer.com
182. The association between cataract surgery and mental health... : International Journal of Surgeryjournals.lww.com
183. Cataract Surgery in Low-Income Countries: A Good Deal!ncbi.nlm.nih.gov
184. Cost-effectiveness of cataract surgery in airis.who.int
185. Cataract Surgery in Low-Income Countries: A Good Deal!mdpi.com
186. The $1 Trillion Blind Spot:seva.org
187. Cost-effectiveness of Surgery in Low- and Middle-income Countries: A Systematic Reviewlink.springer.com
188. Cost Effectiveness Analysis Using Disability-Adjusted Life Years for Cataract Surgerydoi.org
189. Depression and its Association With Cataract Status and Self-Perceived Burden of Elderly Patients With Cataract - PMCpmc.ncbi.nlm.nih.gov
190. Cataract Historynews-medical.net
191. History of cataract surgeryen.wikipedia.org
192. Couching (ophthalmology)en.wikipedia.org
193. The History of Cataract Surgery (A Comprehensive Guide)londoncataractcentre.co.uk
194. Cataract Surgery: Couching to Phaco - American Academy of Ophthalmologyaao.org
195. (PDF) Anatomy of the eye from the view of Ibn Al-Haitham (965-1039). The founder of modern opticsresearchgate.net
196. Book of Opticsen.wikipedia.org
197. graphsearch.epfl.chgraphsearch.epfl.ch
198. Book of Opticsislam.fandom.com
199. Cataract - Etymology, Origin & Meaningetymonline.com
200. cataract - Wiktionary, the free dictionaryen.wiktionary.org
201. CATARACT definition and meaningcollinsdictionary.com
202. CATARACT Definition & Meaning - Merriam-Webstermerriam-webster.com
203. CATARACT Definition & Meaningdictionary.com
204. Cataract or Waterfall: The Etymology of Words in Ophthalmology - OphthoQuestionsophthoquestions.com
205. First patient enrolled in pilot cataract trial assessing lanosterol eye drop ZOC2017217optometrytimes.com
206. Failure of Oxysterols Such as Lanosterol to Restore Lens Clarity from Cataractsncbi.nlm.nih.gov
207. Eye Drops for Cataracts? Human Trials Are Finally Hereeyecarecenteroc.com
208. Can Cataracts Be Reversed? A Closer Look at Lanosterollondoncataractcentre.co.uk
209. Full article: Breaking Barriers: Nanomedicine-Based Drug Delivery for Cataract Treatmenttandfonline.com
210. Nanoparticles in intraocular drug delivery - PMC - NIHpmc.ncbi.nlm.nih.gov
211. Nanomedicine-based Drug Delivery for Cataract Treatmentdovepress.com
212. Nanotechnology for Eye Topical Drug Deliveryencyclopedia.pub
213. Lens regeneration using endogenous stem cells with gain of visual function - PubMedpubmed.ncbi.nlm.nih.gov
214. Cataract surgery is deeply flawed. A new technique could helpstatnews.com
215. Stem cells regenerate human lens after cataract surgery, restoring visionuniversityofcalifornia.edu
216. Lens regeneration in situ using hESCs-derived cells —similar to natural lens - ScienceDirectsciencedirect.com
217. Effective Cataract Surgical Coverage - ICEHiceh.lshtm.ac.uk
218. WHO Urges Faster Expansion of Global Access to Cataract Surgeryeyecarebusiness.com
219. Premium versus Standard Intraocular Lenses for Cataracts: A Review of Clinical Effectiveness and Cost-Effectiveness - NCBI Bookshelfncbi.nlm.nih.gov